Milling and stretching integral panels



Se t. 6 1955 M. s. REED MILLING AND STRETCHING INTEGRAL PANELS FiledJuly 8, 1952 R O T N E V m flamam/JJI feed ATTORNEYS Patented Sept. 6,1955 2,716,806 MILLING AND STRETCHIN G INTEGRAL PANELS Macdonald S.Reed, Erie, Pa. Application July 8, 1952, Serial No. 297,667 6 Claims.(Cl. 29-548) This invention relates to methods of forming metal sheets,and particularly to the forming of thin sheets having integralupstanding ribs, such sheets being commonly referred to as integrallystiffened panels.

It is desirable, especially in the aircraft industry, to have sheets ofrelatively large surface area and quite thin provided with integralupstanding ribs or flanges formed thereon to provide stiffening wherebysuch sheets may be employed as a rigid skin,for the aircraft. Theproduction of such structural sheets has heretofore been impractical byknown methods since the finished sheet requirements, as relating to thethickness of the integral flanges and the heights thereof, is such as torender such shapes impractical to produce by any previously knownmethods. In general, it is desirable that finished sheets of a thicknessof the order of magnitude of inch be provided with integral ribs orflanges of about the same thickness projecting from one surface andspaced apart from 1 /2 to 3 inches. The ribs are desirablyof a height ofthe general order of one inch or more. It can readily be seen thatintegral structural shapes of those dimensions would be extremelydifiicult to produce by conventional methods.

Attempts have previously been made to economically produce integrallystiffened panels of the type described, but none of them have thus farproven successful. Applicant proposes to produce such panels by millinggrooves into the opposed faces of relatively thick metal plates todefine spaced parallel ribs with reversely bent corrugations between theribs. Preferably, the corrugations extend substantially throughout thefull thickness of the original plate. The corrugated sheet thus producedis thereafter stretched in a direction transverse to the ribs to flattenthe corrugations, leaving the ribs themselves upstanding from a surfaceof the resulting panel. The finished product comprises a fiat sheet muchthinner than the original plate with integral upstanding ribs thereon ofa height about equal to the thickness of the original plate. Theflattening of the corrugations may be accomplished by stretching themilled plate, as described, or may be accomplished by other means suchas by pressing or by means of suitably shaped rollers.

By thus milling the intermediate product to a sheet of corrugated form,and later flattening the corrugations, a final product of much greaterwidth than the original mill capacity is possible.

It is, therefore, an object of this invention to provide a method offorming integrally stiffened panels more efficiently and moreeconomically than by methods heretofore known.

Another object of this invention is to provide a method of formingintegrally stiffened panels of practical dimensions from metal plate.

It is still another object of this invention to provide a method forforming sheet material whereby pieces of greater area may be fabricatedthan possible with previously known methods.

A still further object of this invention is the provision of a method offorming an article with conventional apparatus and resulting in aproduct of greater size than the capacity of the appratus to producedirectly.

It is another object of this invention to provide an intermediatestructure by milling or sawing solid metal stock so that the milledintermediate product may be later processed to the desired finishedshape.

Further objects and advantages will appear to those skilled in the artas the description proceeds in connection with the accompanyingdrawings, wherein:

Fig. 1 is an end view of a portion of a metal plate after it has beenmilled to the desired shape;

Fig. 2 is a fragmentary end view of the finished product produced fromthe structure of Fig. 1;

Fig. 3 shows a portion of the metal plate stock in full lines andindicates, by dotted lines, a possible arrangement of milling cuttersand/or saws for producing the intermediate product of Fig. 1;

Figs. 4, 5, 6, and 7, illustrate alternative intermediate products thatmay be cut from thick plate stock to produce dilferent final products.

Referring first to Fig. 2, which is a fragmentary end view of thefinished product, numeral 2 indicates the thin fiat skin previouslyreferred to having integrally solid upstanding ribs 4 projecting fromone surface thereof. Preferably, the material from which these panelsare made is aluminum, aluminum alloy, or a suitable magnesium alloy foruse in covering aircraft frames. Clearly, however, other metals ormaterials may be employed, especially if the product is to be used inother installations than aircraft.

The panel of Fig. 2 was produced from the intermediate product shown inFig. 1. As shown in Fig. l, the the intermediate product consists ofspaced ribs 4 but the skin 2 of the finished ,panel is arranged in theform of a corrugation 6 extending upwardly between the ribs 4. After theintermediate product of Fig. 1 is produced, tension may be applied tothe ends of the skin, as indicated at A. The application of such tensionresults in the flattening of the corrugation 6 to the form shown in Fig.2. After the corrugation assumes a flat condition, the sheet is furtherstretched to slightly exceed the elastic limit of the metal andpermanently setthe panel in the flat condition to which it is drawn. Aswill be obvious, the stretching of the sheet in the manner indicated hasno elfect on the ribs 4 other than to move them apart. As is clearlyevident from the drawings, the ribs 4 are quite close together in theintermediate product of Fig. l, but spaced apart a considerably greaterdistance in the finished product of Fig. 2.

Fig. 3 shows at 8 a solid line representation of a portion of arelatively thick metal plate constituting the stock material of thepresent invention.

Referring again to Fig. 1, the intermediate product consists of a thickplate having grooves 10 cut into one surface thereof and grooves 11 cutinto the opposite surface. Saws or cutters 12 of Fig. 3 may be arrangedon a mandrel 14 to cut the grooves 10 while the saws or milling cutters16 may be arranged on a second mandrel 18 to cut the grooves 11. Thesaws 12 may be spaced apart the required distance by means of spacers 20and auxiliary milling cutters 22. The auxiliary cutters 22 are for thepurpose of forming the curved upper surface 24 of the corrugation 6.Preferably, the saws or cutters 12 and 16 are rounded at theirperipheries to form round bottomed grooves. The mandrel 18 may also beprovided with auxiliary cutters 26 adjacent the cutter 16 for thepurpose of forming the curved surfaces 28 at the bottoms of thecorrugation 6. Spacers 30 may be employed to separate adjacent groups ofcutters 26 and their associated saw or cutter 16.

As is clearly evident from the drawings, the grooves 10 extenddownwardly such a distance that their bottoms are spaced from the bottomsurface of the original plate a distance substantially equal to thespacing between grooves 10 and 11, and since the bottoms of the grooveand the shoulders at the entrances of the grooves are all rounded, thematerial remaining between ribs 4 may be described as a thin platearranged as a corrugation between the ribs. The spacing between grooves10 and 11 determines the thickness of the skin 2 shown in Fig. -2.

The saw and/ or cutter arrangement of Fig. 3 is merely illustrative ofone possible arrangement. Many other forms of conventional millingcutters or saws could clearly be employed to produce the intermediateproduct of Fig. 1. Fig. 3 also suggests the simultaneous cutting of thegrooves in opposite sides of the plate 8 but clearly the grooves cut bythe cutters on mandrel 14 could constitute one operation and the cuttingof the grooves 11 could be a subsequent and separate operation, ifdesired.

Fig. 4 illustrates a modified intermediate product wherein the ribs 4'are considerably thicker than those shown in Figs. 1 and 2 whereas theskin is of substantially the same thickness. The apparatus suggested inFig. 3 may be readily adjusted for the production of the Fig. 4 productby merely increasing the thickness of the spacers 2t) and 30, theremainder of the set-up remaining the same.

Fig. 5 illustrates a still further modified form of intermediate productwherein the corrugation 6 is formed to extend a substantial distanceabove the tops of the ribs 4.

Such an intermediate product results in a final product similar to thatof Fig. 2 but wherein the ribs 4 are spaced apart a materially greaterdistance since the length of sheet material comprising the corrugation6' is greater than the length of material comprising the corrugation 6of Fig. 1.

Fig. 6 shows a still further modified form of intermediate productcomprisnig the spaced ribs 4 but wherein a pair of corrugations 32 and34 are formed between adjacent ribs. Fig. 5 was described as a method ofincreasing the spacing between the ribs 4 but it is clear that thatmethod has limitations since it involves the waste of a greater amountof material than the method of Fig. 1. All of the material above theribs 4 must be removed and is lost. When it is desired to produce afinal product having the rib spacing substantially greater than ispossible with the method of Figs. 1 or 5, the intermediate product ofFig. 6 may readily be produced. It will be evident that when theintermediate product of Pig. 6 is stretched to its final form, thespacing between ribs 4 will be substantially twice that shown in Fig. 2while the thickness of the skin 2 and the height and thickness of ribs 4remains the same.

The intermediate product of Fig. 6 may also be readily produced by amere addition of cutters of Fig. 3, it being only necessary to addadditional saws and auxiliary cutters between the saws 12 that definethe sides of the ribs 4 and the addition of an additional cutter 16 andauxiliary cutters 26 on mandrel 18. The cutters 12, 22, 16, and 26 mayall be identical and of standard proportions.

The most economical and desirable intermediate prod net is of the typeshown in Figs. 1, 4, and 6, wherein the crests of the corrugations liein the same plane as the tips of ribs 4, that plane being the originalupper face of the stock plate 8. Thus, the least amount of material needbe removed to produce the intermediate product.

Fig. 7 shows another modified form of intermediate product comprisingspaced ribs 4 and an upstanding corrugation 40 of less height than theribs 4. The corrugation 40 is provided, on its crest, with a rib orprojection 42. Obviously, this intermediate product may be readilyproduced by the same operations described in connection with theprevious embodiments and when stretched or flattened to a shapecomparable to that of Fig. 2 the rib or projection 40 will remain as anupstanding rib in the finished product located centrally between ribs 4but of much less height. Clearly, the auxiliary or shortened ribs 42 mayalso be provided on such structures as illustrated in Fig. 6, whereinmore than one corrugation is formed between the major or principal ribs4.

While applicant has referred herein to milling cutters and saws, it isto be understood that the term is intended to include any and allcutting tools capable of producing the shapes described or other obviousor equivalent shapes and might conceivably even be shaper cutters, andmills, or the like.

While a single specific method has been shown and de-- scribed herein,it is to be understood that the same is merely illustrative of theinvention and not intended as a limitation. Many modifications andchanges may be resorted to which fall fairly within the scope of theappended claims.

I claim:

l. A method of forming an integrally stiffened panel, comprising thesteps of: milling opposite faces of a relatively thick metal plate toprovide spaced integral ribs on one side and at least one corrugationbetween said ribs, and thereafter flattening said corrugations to produce a wider and substantially flat panel of less thickness than saidplate having spaced parallel solid integral ribs upstanding from onesurface thereof.

2. A method as defined in claim 1, wherein said corrugations areflattened by stretching said milled sheet in a direction transverse tosaid ribs.

3. A method of forming an integrally stiffened panel, comprising thesteps of: milling a first set of spaced grooves in one face of arelatively thick metal plate; milling a second set of spaced grooves inthe opposite face of said plate, the grooves of said second setextending between certain but less than all of the grooves of said firstset whereby to provide spaced solid ribs ex tending to said one face,and at least one corrugation between adjacent ribs, and thereafterflattening said corrugations to produce a wider and substantially flatpanel of less thickness than said plate having spaced solid integralribs upstanding from one surface thereof.

4. The method defined in claim 3, wherein said flattening step isperformed by placing said milled plate under sufficient tension, in adirection transverse to said ribs, to flatten said corrugations andthereafter to stretch said fiat panel slightly beyond its elastic limit.

5. A method of forming an integrally stiffened panel, comprising thesteps of: milling a first set of spaced pairs of parallel grooves in oneface of a relatively thick metal plate; milling a second set of spacedparallel grooves in the other face of said plate, each of the grooves ofsaid second set being milled to extend between the grooves of said pairof grooves in said one face, the material be tween said pairs of groovesdefining ribs extending toward said one face, each of said grooves beingmilled to a depth sufficient to space their bottoms from the oppositeface of said plate a distance substantially equal to the spacing betweenadjacent grooves; and defining corrugations between said ribs,thereafter flattening said corrugations by placing said milled plateunder sufficient tension, in a direction transverse to said ribs, toflatten said corrugations and thereafter to stretch said flat panelslightly beyond its elastic limit.

6. A method of forming an integrally stiffened panel, comprising thesteps of: cutting a first set of spaced pairs of grooves in one face ofa relatively thick metal plate; cutting a second set of spaced groovesin the other face of said plate, each of the grooves of said second setbeing parallel to and cut to extend between the grooves of said pair ofgrooves in said one face, the material between said pairs of groovesdefining solid ribs extend ing toward said one face, each of saidgrooves being cut to a depth to space their bottoms a substantialdistance from the opposite face of said plate; and defining corrugationsbetween sail ribs, thereafter flattening said corrugations by placingsaid cut plate under sufficient tension, in a direction transverse tosaid ribs, to flatten said corrugations and thereafter to stretch saidpanel slightly beyond its elastic limit.

References Cited in the file of this patent UNITED STATES PATENTS1,623,273 Rendleman Apr. 5, 1927 2,018,085 Otte Oct. 22, 1935 2,263,425McKee Nov. 18, 1941 2,615,234 Dumbleton Oct. 28, 1952 2,617,179 BurkeNov. 11, 1952

